1. Field of the Invention
The present invention relates to a high-frequency switch, and more particularly to a high-frequency switch for being incorporated in a mobile communications device and the like.
2. Description of the Related Art
A high-frequency switch is generally used for switching between a transmission circuit and a reception circuit in a digital mobile telephone and the like. FIG. 6 is an electrical circuit diagram showing a prior art high-frequency switch 1. The anode of a diode D1 is connected to a transmission terminal Tx. The anode of the diode D1 is grounded via a series circuit comprising a transmission line 2 and a DC-blocking capacitor C1. A voltage-control terminal Vc1 is connected via a resistor Ra at an intermediate connection point between the transmission line 2 and the capacitor C1. The cathode of the diode D1 connects to an antenna terminal ANT.
A reception terminal Rx is connected to the antenna terminal ANT via a transmission line 3. Moreover, the anode of a diode D2 is connected to the reception terminal Rx. The cathode of the diode D2 is grounded.
Here, the DC-blocking capacitor C1, connected between the transmission line 2 and the ground, has a large capacitance (approximately 47 pF near 1 GHz, and approximately 22 pF near 2 GHz). Since the size of the capacitor C1 connected between the transmission line 2 and ground is large, miniaturization of the high-frequency switch 1 is hindered.
Furthermore, in the high-frequency switch 1, when the transmission terminal Tx and the antenna terminal ANT are connected, isolation must be maintained between the antenna terminal ANT and the reception terminal Rx. When this isolation is poor, insertion loss between the transmission terminal Tx and the antenna terminal ANT increases.